NKG2A is a marker for acquisition of regulatory function by human CD8+ T cells activated with anti-CD3 antibody

Treatment with anti-CD3 mAb modulates immune responses that cause type 1 diabetes and other diseases. CD8(+) Tregs can be induced in vitro and in vivo by mAb. However, 1/3 of patients do not respond to drug therapy and in an equal proportion, anti-CD3 mAb does not induce Tregs in vitro. The acquisition of CD8(+) Treg activity is a function of the CD8(+) cells and not the targets in the assay. To identify markers to differentiate responses of CD8(+) Tregs, we analyzed genes differentially expressed in CD8(+) T cells of non-responders compared with responders, and found that an inhibitory receptor NKG2A (CD159a) was highly expressed in cells from all non-responders tested. Application of a mAb agonistic to NKG2A during in vitro CD8(+) Treg induction by anti-CD3 prevented induction of CD8(+) Tregs. CD8(+) T cells that are TNFR2(+) but NKG2A(-) are the most potently induced Tregs. The level of NKG2A expression on resting CD8(+) T cells inversely correlated with acquisition of regulatory function when activated. We suggest that the induction of human CD8(+) Tregs by anti-CD3 mAb is controlled by a negative signaling through NKG2A, and that NKG2A may serve as a negative marker of human CD8(+) Tregs.